An estimated170 million people worldwide and 20 million Americans are infected with hepatitis C virus HCV). Although some individuals clear the infection, many progress to chronic disease and years later can get liver cancer. Since 85% of liver cancers are HCV-associated, if infection could be avoided by vaccination, this would have a major impact on the incidence of liver cancer. My hypothesis is that new vaccines against HCV can be generated based entirely on selecting synthetic B cell epitopes recognized by already-existing neutralizing monoclonal anti-HCV antibodies that we are fortunate to have. I believe that the best choice for a library of B cell epitopes is peptoid rather than peptide-based. Peptoids are oligomers of N-substituted glycines not restricted to the 20 natural amino. The side chains are simple primary amine derivatives, hundreds of which can be purchased inexpensively as compared to peptides. Peptoids are protease resistant, can use D amino acid side chains (peptoid-hybrids), and can also be cyclic. Peptoids are structurally similar to peptides but are protease resistant, can be created in more diverse shapes to fit into the binding pocket of B cell receptors, and are easily and inexpensively synthesized in large amounts. They can be generated with a theoretical diversity of 107 or greater and a "working diversity" of a million. They are haptens and need not contain T cell epitopes. Finally, while conserved neutralizing epitopes on HCV might not be immunodominant, or might be sparse, in our platform, epitope mimetics should be immunodominant since they are haptens and many copies will be attached to a carrier protein. The carrier protein will provide T cell help to induce robust, high affinity IgG responses against the peptoid. Hence, T cell help will not be restricted to individuals with certain HLA haplotypes. We have already shown that peptoids conjugated to carrier proteins are highly immunogenic and that, in a model system, they can induce antibodies that also react with the native peptide. In this proposal we plan to use a panel of neutralizing monoclonal antibodies (MAbs) against HCV for screening. Those peptoids that are positive in the screen will then be sequenced, synthesized in bulk, and tested for their ability to block the binding of the native E2 protein of HCV to the screening MAb Those that block at the lowest concentration will be conjugated (together or separately) to a carrier protein, mixed with alum (an adjuvant approved for humans), and used to immunize mice. The mouse sera will be tested for reactivity against E2. Those that react will be further tested for their ability to neutralize a panel of HCV genotypes. Although other mimetic platforms have not met with great success, we believe that the peptoid platform overcomes many of the problems associated with other mimetics such as peptides, carbohydrates and anti- idiotypic antibodies, and that it holds great promise as a vaccine platform for HCV and other pathogens. PUBLIC HEALTH RELEVANCE: The objective of this grant is to generate an effective vaccine against Hepatitis C virus, the major cause of liver cancer. Our vaccine platform is based on synthetic structures called peptoids that are selected by existing monoclonal antibodies that are already known neutralize the virus. These peptoids will be screened with these antibodies, and those that react will be coupled to carrier proteins and used to immunize mice. The mice should make antibodies that then both recognize both the peptoid and the virus.